1. Field of the Invention
The present invention relates in general to an image taking system and more particularly to the art of taking images with stable brightness.
1. Discussion of Related Art
There is known an image taking system which is employed in an electric-component mounting system for mounting electric components (in particular, electronic components) on a printed-wiring board, and which takes an image of an electric component held by an electric-component holder and detects, based on the taken image, a position, a posture, a shape, and/or a type of the electric component. The conventional image taking system usually includes an illuminating device and an image taking device, and repeats image taking actions by controlling those devices under pre-set control conditions. While the illuminating device is new, the device can emit a light having a sufficiently high intensity. However, as time elapses, a light source of the illuminating device deteriorates, and the intensity of light emitted by the device decreases. If the image taking system employing the light source which deteriorates as time elapses, repeats image taking actions under the preset control conditions, respective images repeatedly taken by the system will be gradually darker as the intensity of light emitted by the light source decreases. If a taken image is dark as a whole, it is difficult to accurately determine, in the image, a boundary line between a bright area and a dark area, i.e., an edge line between the object (the electric component) and its background. If the light source has deteriorated and the intensity of light emitted thereby has decreased, the light source may be exchanged with a new one. In this case, however, the frequency of exchanging of light sources increases, which leads to increasing the running cost of the image taking system. In addition, since the operation of the image taking system and accordingly the electric-component mounting system must be suspended when the light sources are exchanged, the operation efficiency of the mounting system decreases.
The above explanation is not limited to the image taking system employed in the electric-component mounting system, but applies to other image taking systems.